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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

37

out into a 200 c.c. flask, made up to volume, mixed and filtered through a
dry filter.

By means of a pipette corresponding exactly with the measuring-flask,
100 c.c. of the filtrate (= 3 grams of substance) are introduced into a 300
c.c. beaker already containing 10 c.c. of potassium carbonate solution of
density 1-490 (66 grams of anhydrous carbonate in 100 c.c. of solution).
After mixing, the liquid is slowly heated and finally boiled for 20-25 minutes
until effervescence ceases and the whole of the calcium carbonate thrown
down in powder.1 After cooling to the air-temperature, the liquid and
precipitate are poured into a 200 c.c. graduated flask, the beaker being
washed repeatedly with distilled water. After making up to volume and
mixing, the liquid is filtered through a dry, pleated filter, and 100 c.c. of
the filtrate (= 1-5 gram of substance) evaporated on a steam-bath in a
400-500 c.c. porcelain dish until the crystalline skin forming at the edges
no longer dissolves on gentle shaking. The evaporation is continued for
some minutes with movement of the dish until a dry residue is obtained.
This is redissolved in 5 c.c. of boiling water and 4 c.c. of glacial acetic acid
then added in drops at the edge of the hot liquid, the whole being stirred
vigorously for 5 minutes with a glass rod. After a further interval of 10
minutes, 100 c.c. of 95% alcohol are added and the mixture stirred for 5
minutes to render the precipitate granular and crystalline.

After the lapse of 10 minutes, the alcohol is decanted on to a cellulose
filter and drawn through with a pump. The precipitate is washed three or
four times with alcohol by clecantation, then introduced on to the filter
and the washing continued until the alcohol passing through no longer
exhibits an acid reaction.

The filter and precipitate are placed again in the dish with 200-300 c.c.
of water, boiled for a minute, and titrated in the hot with N/4-potassium
hydroxide (standardised with puriss. bitartrate), neutral, sensitive litmus
paper being used as indicator. The number of c.c. of alkali used, multiplied
by 10 and divided by 4, gives directly the percentage of tartaric acid.

The result obtained must be corrected for the volume occupied in the
solutions by the insoluble substances. Where 12 grams of material are
taken, the correction is calculated by means of the formula,

y = i o-oi x,

where x is the percentage of tartaric acid found and y the amount to be
deducted from it ; if 6 grams are taken, the correction is one-half that given

by the above formula.

*

* *

Wine lees usually contain from 15 to 30% of potassium bitartrate, but some-
times as little as 10% or as as much as 40% ; the Italian products generally
contain about 24% of tartaric acid as potassium bitartrate and about 6% as
calcium tartrate. Cask incrustations contain up to 70-80% of cream of tartar,
and crude tartar contains more or less according to the method of preparation ;

1 According to Perciabosco (Stan. agr. Hal., 1914, XLVII, p. 803), with material
rich in, tartratea it is advisable to add the potassium carbonate to the boiling hydrochloric
acid solution. In this case the boiling is protracted after the addition of the carbonate
for only 10 minutes.ith ammonia and treated with ca^iiim